Air filter



Patented Oct. 2, 1951 UNITED STATES PATENT GFFICE AIR FILTER Thomas E. Philipps, Granville, Ohio, assignor to glasCorporation, a corpo- Owens-Corning Fiber ration of Delaware This invention relates to lters for separating out solid particles, such as dust from air or other gaseous media. More particularly, the invention relates to a dust catching adhesive or air filtering material on a porous base, such as a glass ber base, through which the gaseous medium flows.

A desirable dust catching adhesive should be inexpensive, odorless and have a large dust collecting capacity. It has been found that the adhesive is effective while it remains relatively soft or in semi-fluid condition, thus solidication at low temperature or crystallization at low humidities causes substantial failure in operation. On the other hand, the efficiency of the filter is impaired if the material becomes so uid at elevated temperature or high humidities as to run or bleed from the base fibers. Of further importance is the reaction of the adhesive to high temperatures and llames; that is, it should be non-inflammable and non-combustible and should not create fumes or smoke of such volume, density or kind as to be toxic or incite a panic.

Referring brieiiy to the adhesive materials that have been used, petroleum oils, bodied or unbodied, and with or Without bodying agents, such as soaps, have been employed but they are objectionable because they not only slowly run or bleed from the base but also the oily substances are inflammable. Flame-proof chlorinated compounds, such as chlorinated diphenyl, have been added to these oils, but, when used in amounts to be effective'in reducing the combustibility of the adhesive, they form a sludge or solid mass with oil, which as previously pointed out, is undersirable.

Use has been made of the deliquescent salts or metal halides, such for example as zinc chloride, tin chloride or lithium chloride, but these materials are corrosive to metal frames and duct Work, presence of moisture, and may crystallize out at very low humidities. Organic esters of phosphoric acid, such as tricresyl phosphate, although not combustible, decompose at elevated temperatures and phosphorous in the form of phosphorous pentoxide (P205) appears as a part of the decomposition products. These dense White fumes have been known to cause greater panic than might have resulted from a visible ilame.

An object of this invention is to produce a dust catching adhesive which is inexpensive, odorless, non-corrosive, has a large dust catching capacity, and has the additional features of being relatively free from the objections to the materials heretofore used.

Another object is to produce a Wholly non-combustible, non-inflammable adhesive, the decomposition products of which do not form dangerous vapors or fumes.

A further object is to produce a liquid dust catching material, which is relatively insensitive to changes in temperature and humidity so that it maintains its effective condition on the supporting base.

A still further'object is to produce a dust catching adhesive based on a non-combustible phosphorous containing compound constituted with ingredients capable of reacting With the phosphorous at decomposition temperatures substantially to prevent its release to the atmosphere.

It has been discovered than an organo-metallic (organo-inorganic) salt of an acid of phosphorous is a material having the properties desired in a non-combustible, non-fuming, odorless, low cost and eilicient dust catching adhesive. These might also be referred to as inorganic esters or organo-metallic esters of an acid of phosphorous. When the phosphorous is present as the phosphate, the organo-metallicV salt may be represented by the formula RnMs-POn Where R is a monovalent organic radical or derivative thereof represented by the aliphatics, such as methyl, ethyl, propyl, butyl, isobutyl, amyl and others; aromatics and mixed aliphatic-acromatics, such as phenyl, benzyl, tolyl, xylyl, ethylphenyls, naphthyls, phenylethyls and the like; alicyclics and heterocyclics, such as cyclopentyl, cyclohexyl, furfuryl, and the like. When aliphatic, the group may be saturated or unsaturated, substituted or unsubstituted. M preferably is an alkali metal of the type lithium, sodium, potassium and the like but may also be ammonia or an amine or mixtures of these with the metals, and n is either 1 or 2, unless M is an amine, such for example as mono-, di-, or triethanolamine, in which case n may be zero.

Representative of suitable organo-metallic salts of phosphoric acid are; di-methyl sodium phosphate, di-ethyl sodium phosphate, methyl ethyl potassium phosphate, methyl ethyl sodium phosphate, sodium ethyl potassium phosphate, methyl potassium sodium phosphate, di-sodium butyl phosphate, methyl di-sodium phosphate, ethyl cli-potassium phosphate, iso-butyl sodium ethyl phosphate, ethyl sodium ammonium phosphate, methyl sodium ammonium phosphate, methyl potassium ammonium phosphate, ethyl triethanolamine potassium phosphate, methyl triethanolamine potassium phosphate, ethyl triethanolamine ammonium phosphate, methyl triethanolamine ammonium phosphate, ethyl triethanolamine sodium phosphate, methyl triethanolamine sodium phosphate, methyl trietl'ianolamine phosphate, triethanolamine phosphate, triethanolamine ammonium phosphate, phenyl triethanolamine sodium phosphate.

The preferred salts are water soluble andliquid under 'odinary'atmospheric conditions. Application'thereof is made to the base by ordinary means such as ow coating, spraying, dip-squeezing and the like from an aqueous solution in which the concentration of the salt may be varied from 20 to 75 per` cent by weight, a satisfactory deposit being made from about a 60'per`cent solution. The organo-metallic salt generally remains liquid after the diluent has been driven off and in that condition readily wets` the surfaces of the glass bers so that a stable and effective iilter is secured. Furthermore, the inherently smooth surfaces of the glass bers provide little resist- 'ance to the iiow of the ,gaseous medium, vwhile little adhesiveY is actually'required thoroughly to saturatthe ber surfaces because these glass fibers are non-absorbent.

f Some of the'adhesive materials are more hycrystallization at low-'humidities may be elimi- :1.

hated-and the absorption of water reduced if a polyliydric alc'zoholfsuch as glycerine, ethylene glycol, trimethylene glycol, tetramethylene glycol andthe-like',` and "especially if polymers thereof 'are incorporated with the "organo-metallic salt. L

Preferred glycols are the polyethylene glycols, commercially knownv as Carbo'wax, produced by theCarbi'de andv Carbon Chemical Corporation of- New York, New York; The use of polymers of less than 1000 molecular weight is most desirable'becau'se they are liquid at room conditions andare 'able to operate also as a solvent for the rgano-metallic salts of phosphorous, in which manner they are believed'to prevent crystallization at low humidity.

InA specific'fapp'lication, the adhesive may be composed of 2-parts of the organo-metallic salt to l; part'- of the polyhydric alcohol, althoughv as much as equal parts of each have been successfully used and, where the metallic component in the salt is less, less of the polyhydric alcohol may be used. It may be entirely eliminated when an amine or organo-ammonium phosphate is employed because neither of, these crystallizes at lowhumidities. The hygroscopicity of the phosphoric acid esters, such as tricresylV phosphate, has been effectively reduced by the presence of these polyhydric alcohols and polymers thereof.

' In actual practice, the glass iibers of the base are readily wet by the non-iniiammable organicinorganic salt of phosphoric acid, and, in View of the great amount of Vsurface area made possible by the use`of glass fibers, an eiiicient filter is produced. As previously pointed out, most of these salts remain liquid at any humidity, and if not, non-volatile liquid alcohols, which dissolve the salts and maintain them inliquid form, are incorporated; These salts are quite stable up to temperatures which cause' the breakdown or, eltlzaqn f the Organic, groups, "Such wat 450 F. At such relatively high temperatures, the metallic constituents seem to combine with the phosphorous to form more stable salts or what appears as a new glassy phase, effectively to tie up the phosphorous so that very little escapes to the atmosphere. Otherwise, the phosphorous would come forth as dense white fumes of P205, which in 4 crowded quartersare .frightening and have been known to cause disastrous panics.

Thus there is produced an efficient filter composed of an inert base, which oiers little resistance to the flow of the gaseous medium, and adhesive material, which is for the most part noncombustible and non-fuming, it being understood vthat y.the decomposition products of the small amountn oforganic-matter are not in sufficient concentration to produce a lasting flame.

.Thisv invention is not limited to the application of these dust catching adhesives to bases or "media formed only of glass fibers, but other porous bases f ormed of a combination of glass fibers with other materials or formed exclusively of other materials such as metal, paper, cellulosic materials'or other iiltering media may also ,be used.

Preferably the filter medium is in the form of a pad or mat of substantially less thickness than width and length. This pad is enclosed between grillesorVY perforated' metal or paper facings that overlie the major lfaces of the pad. The air to be ltered passes in turn through one of the grilles, the inlet grille, through the p'ad in the direction of its thickness, and out through the other grille, the'ou'tlet grille." The padand grilles are usually secured together by a frame or container that encloses Athe edges and margins of the pad and grilles. An air lter'unit of this'typ'e is shown in the Myers Patent No. 2,077,951.

For example, on Ythe accompanying drawing:

FigureY 1 is a perspective view of oneforxn the unit or "container of the present inventionI may take,`and"' Figure'Z is a cross-section of Figure l taken on theline 2-2. Referring to these figures, a pad or mat of glass fibers I0 containing a dust catching adhesive of the present invention is enclosed between two similar, parallel grilles I I and I2. The entire assembly is then secured as by stapling to a cardboardy frame I3 which covers the edges and margins'of the pad and grilles.v If desired, a paper tape may be adhered to the unit around its perimeter to impart further rigidity.

It is to be understood that various modifications of materials and concentrations may be made Without departing from the scope of the invention especially as defined in the following claims.

.I claimz,

1'. Aiilter comprising a porous filtering base, and a dust catching adhesive on said base 'in the form of-'an 'organo-inorganic salt of an acid ofphosphorouls.

' 2.'A gaseous lter comprising a gaseous permeable base 'of glass'bers, and a coating on'the.

` '4.' A lter comprising a porous base'withglass'v fibers, and an mpregnant interspersed throughout the porous base and comprising a compound represented by the formula Rum-P04 in which R is a monovalent organic radical, M is an inorganic selected from the group consisting of an alkali metal, ammonia and an amine and n is an integer between 1 and 2 unless M is an amine in which case n may be zero.

5. A iilter material comprising a glass fiber i base, and a coating on the fibers composed of a solution containing a water soluble phosphate represented by the formula RnM-POr in which R is a monovalent organic radical, M is an alkali metal, and n is an integer between 1 and the numeral 2, and a solvent for said phosphate selected from the group consisting of polyhydric alcohols and polymers thereof.

6. A filter material comprising a glass fiber base, and a liquid coating on the bers consisting of an organo-inorganic salt of an acid of phosphorous and a polyhydric alcohol.

7. A lter material comprising a glass fiber base, and a liquid coating on` the bers consisting' of an organo-inorganic salt of an acid of phosphorous, and a polymer .of a polyhydric alcohol.

8. A filter material as claimed in claim 7, in which the ratio of the polymer of the polyhydric alcohol to the salt is less than 2 to 3.

9. A gas filter comprising a porous fibrous base and a liquid coating thereon of a composition containing an organo-metallic ester of an acid of phosphorous and less than 30 per cent by weight thereof of polyethylene glycol.

10. An air filter material comprising a base of glass fibers and a composition on the surfaces of the bers consisting of a phosphoric acid ester and a polyglycol.

1l. A filter unit comprising a container, an air-pervious face through which air to be filtered enters the container and a second air-pervious face through which iiltered air leaves the container, and a filtering medium between said per- Vious faces composed of lglass fibers coated with an organo-metallic salt of an acid of phosporous 4 represented by the formula BaMa-P04 in which R is a monovalent organic radical, M is an inorganic selected from the group consisting of an alkali metal, ammonia and an amine and n is an integer between 1 and 2 unless M is an amine in which case n may be zero.

12. A dust lter comprising a porous filtering base of glass fibers and a dust collecting adhesive on the glass ber surfaces consisting essentially of a water soluble organo metallic salt of an acid of phosphorous in which the organic group is selected from the monovalent groups consisting of aliphatic, aromatic and mixed aliphatic-aromatic radical in which the aromatic group is based upon a single ring structure and in which the aliphatic is a lower aliphatic group.

13. A dust filter comprising a porous filtering base of glass fibers and a dust collecting adhesive on the glass fiber surfaces consisting essentially of an organoealkali metal salt of an acid of phosphorous.

14. A dust filter comprising a por-ous filtering base of glass fibers and a dust collecting adhesive on the glass ber surfaces consisting essentially of a lower aliphatic-inorganic salt of an acid of phosphorous.

THOMAS E. PHILIPPS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,071,353 Morgan Feb. 23, 1937 2,083,132 Williams et al June 8, 1937 2,122,514 Crocker July 5, 1938 2,128,782 Muller Aug. 30, 1938 2,145,898 Simpson Feb. 7, 1939 2,178,614 Slayter Nov. 7, 1939 2,262,634 Cobbs Nov. 11, 1941 2,353,936 Smith July 18, 1944 2,415,113 Seymour et al. Feb. 4, 1947 FOREIGN PATENTS Number Country Date 365,012 Great Britain Jan. 14, 1932 

1. A FILTER COMPRISING A POROUS FILTERING BASE, AND A DUST CATCHING ADHESIVE ON SAID BASE IN THE FORM OF AN ORGANO-INORGANIC SALT OF AN ACID OF PHOSPHOROUS. 